This application claims the priority of Japanese Patent Application Nos. 10-78351 and 10-78352 filed on Mar. 10, 1998 which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic-endoscope controlling the quantity of light, and in particular, to the contents of light-quantity control for compensating for the lack of light quantity caused by the setting of a shielding period using an electronic endoscope executing an all-pixel reading system that uses the shielding period to read out all pixels accumulated in an image pickup device.
2. Description of the Prior Art
In an electronic endoscope apparatus, for example, CCD (Charge Coupled Device) is used as a solid image-pickup device, and this CCD is structured so as to obtain an image signal (video signal) by reading out charge accumulated in units of pixels by a photoelectric conversion device. In a simultaneous type electronic endoscope apparatus for example, color filters are arranged in units of pixels on the top surface of the forgoing CCD to thereby obtain a color image.
FIG. 9 shows an arrangement state for the forgoing color filters, and Mg (magenta) and Cy (cyan) pixels are arranged on an even line for example, andG (green) andYe (yellow) pixels are arranged on an odd line on a picked-up surface of CCD1 as shown. In this CCD1, accumulated charge (pixel signal) in units of pixels is to be obtained through these color filters.
According to a conventional color difference line sequential mix reading (pixel mix reading) system, accumulated charges of pixels on the upper and lower lines are added and mixed to be read out. For example, during the first exposure, video signals of such odd field as a mixed signal of 0-line and 1-line, a mixed signal of 2-line and 3-line, . . . are read out, and during the second exposure, video signals of such even field as a mixed signals of 1-line and 2-line, a mixed signal of 3-line and 4-line, . . . are read out. Therefore, two lines of mixed signals of CCD1 become one line of signals of field image, and one odd or even field of data are to be obtained by one exposure.
FIG. 10 shows an operation of signals read out from the foregoing CCD1, and in an electronic endoscope apparatus, an odd field and an even field are formed on the basis of the O (Odd)/E (Even) signal (field signal) for each 1/60 second (vertical synchronizing period) as shown in FIG. 10(A). Therefore, as shown in FIG. 10(B), signals are accumulated in accumulation (exposure) time T of an electronic shutter during the forgoing period of 1/60 second, and the accumulation mixed signal is read out during the next 1/60 second period. As a result, as shown in FIG. 10(C), an odd field signal, and an even field signal are to be obtained, and for example, the (n-1)th odd field signal becomes mixed signals of (0+1) line, (2+3) line, (4+5) line . . . which are shown on the left of FIG. 6, and the n-th even field signal becomes mixed signals of (1+2) line, (3+4) line, . . . which are shown on the right of FIG. 9.
These odd field signals and even field signals are interlace scanned to be formed as a one-frame image, and this image is displayed as a moving image on a monitor. Also, in the endoscope apparatus, a freeze switch is arranged in the operating unit, and when this freeze switch is depressed, a still image at the time is formed and displayed.